All in the Stream

Fever and tachycardia support an infectious cause of his symptoms. Absent flank tenderness and a normal genitourinary examination have only moderate negative predictive values for acute pyelonephritis and prostatitis, respectively. The most striking laboratory finding is his azotemia. Acute kidney injury (AKI) is more likely than chronic kidney disease (CKD) given that the PTH level is normal and the serum creatinine from a year ago was near normal. The most useful finding to differentiate AKI from CKD is the presence of atrophic kidneys on imaging. The low bicarbonate level indicates a metabolic acidosis. His serum anion gap is 13 mEq/L, which falls above most normal ranges. A mildly elevated serum anion gap together with a “delta serum anion gap/delta serum bicarbonate” ratio less than one suggest concomitant anion gap metabolic acidosis and non anion gap metabolic acidosis. The latter, coupled with a history of nephrolithiasis, may point to the possibility of renal tubular acidosis and AKI caused by urinary tract obstruction. This could also account for the marked hyponatremia. Moreover, his high fractional excretion of sodium (9%) is not suggestive of prerenal injury, the most common acute renal injury among patients who present to the emergency department. Hematuria carries a broad differential diagnosis, but most common causes include nephrolithiasis, urinary tract infection (UTI), prostatitis, neoplasm, and glomerulonephritis (GN). The lack of casts and dysmorphic RBCs makes GN unlikely. Taken together, his vital signs, examination, and laboratory studies suggest a high likelihood of an upper UTI (acute obstructive pyelonephritis) in the context of AKI due to obstructive uropathy.

Despite both a normal serum WBC count (which has only a moderate negative predictive value) and his low risk of developing life-threating organ dysfunction from sepsis based on a quick Sequential Organ Failure Assessment (qSOFA) score of zero, it is appropriate to start antibiotics after drawing blood and doing urine cultures. The next step should include administration of a broad-spectrum regimen that is appropriately dose-adjusted for renal dysfunction, such as an antipseudomonal carbapenem and vancomycin to cover extended-spectrum beta-lactamase (ESBL)-producing organisms, Pseudomonas aeruginosa, and methicillin-resistant Staphylococcus aureus (MRSA). This broad coverage is indicated for empiric treatment of complicated obstructive pyelonephritis, a condition that may arise from significant urinary obstruction and that carries a high risk of rapid clinical deterioration. He should undergo a rapid bedside test to assess for urethral or bladder outlet obstruction: either a bladder ultrasound or temporary insertion of a bladder catheter. He should also have an urgent computed tomography (CT) of his abdomen and pelvis without intravenous (IV) contrast, looking for evidence of urinary tract obstruction. A CT is preferred over ultrasound of the kidneys and bladder as CT has higher sensitivity and specificity for nephrolithiasis and neoplasm.

A CT of the abdomen and pelvis without IV contrast revealed bilateral hydroureter and hydronephrosis with multiple punctate calcified stones within the right calyces and the distal right ureter (Figure 1, Figure 2). However, these appeared too small to cause the degree of obstruction visualized. There were no stones noted in the left ureter to account for the obstruction, though small stones were noted in the left calyces. The bladder appeared normal.

Rarely are both ureters obstructed proximal to the ureterovesical junctions in the retroperitoneum. When they are, CT scans usually reveal culprit lesions that are extrinsic to the urinary tract, such as masses or retroperitoneal fibrosis, the latter of which can be associated with IgG4-related disease. Intrinsic causes of urinary tract obstructions include ureteral strictures (from infections, nephrolithiasis, instrumentation, prior radiotherapy, or rarely urothelial cancer), blood clots, metastatic ureteral deposits, or nephrolithiasis. While most intrinsic causes are unilateral, the patient is predisposed to strictures given his history of ureteral instrumentation. A preexisting unilateral obstruction due to a stricture may now, therefore, be unmasked by a second intrinsic obstruction in the contralateral ureter. Alternatively, given his remote history of living in the Philippines, a site where Schistosoma haematobium is endemic, chronic genitourinary schistosomiasis may have caused ureteral strictures due to granulomas, fibrosis, or pseudopolyps.